Rubber aircraft parts

ABSTRACT

Rubber aircraft parts are made of the cured form of a curable composition comprising a perfluoropolyether polymer having a perfluoropolyether backbone and at least one reactive group, a crosslinking agent for crosslinking the polymer, and a silica filler having an average particle size of 0.001-10 μm. By providing dramatically improved sealability at low temperatures of −25 to −55° C., particularly during use in a dynamic state, and much improved resistance to amines and other chemicals, such rubber parts can ensure the reliable sealability of fluid line junctions in jet engines.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to rubber parts for aircraft. Moreparticularly, it relates to rubber parts used as sealing components(e.g., aircraft O-rings, packings, gaskets, face seals) which come intocontact with substances such as engine oil and jet fuel.

[0003] 2. Prior Art

[0004] Rubber parts for aircraft, especially those used as fluid sealingcomponents around jet engines, include O-rings (e.g., fluid lineO-rings), seals (e.g., face seals, packings, gaskets), diaphragms andvalves for aircraft engine oils, jet fuels, hydraulic oils and aviationhydraulic fluids such as Skydrol.

[0005] During use, such rubber parts often inevitably come into contactwith fluids used in aircraft, such as engine oils (e.g., Mobil 254), jetfuels, hydraulic oils, and aviation hydraulic fluids such as Skydrol. Toensure normal operation, these aircraft parts are required to beresistant to jet fuels, resistant to carboxylic acids that arise fromthe oxidative degradation of synthetic oils (e.g., engine oils),resistant to amines and oils, and also resistant to gas permeability,heat and water. In addition, because aircraft are commonly operated incold regions and at altitudes where low temperatures prevail, suchrubber parts must also have a good cold resistance.

[0006] Hence, these aircraft parts are generally made of such materialsas vinylidene fluoride-propylene hexafluoride copolymer-basedfluororubbers, vinylidene fluoride-ethylene tetrafluoride-perfluorovinylmethyl ether copolymer-based cold-resistant fluororubbers, orfluorosilicones.

[0007] Vinylidene fluoride-propylene hexafluoride copolymers, thoughendowed with excellent heat resistance, resistance to oil and gasoline,and flexing resistance, lack sufficient cold resistance. The lower limitin their service temperature is −20° C. for static sealing applications,and −10° C. for dynamic sealing applications (e.g., diaphragms). Inaddition, such copolymers undergo considerable swelling in alcohols andketones, becoming unfit for use thereafter. They are also subject tosevere deterioration by amine-based additives in lubricating oils.

[0008] Vinylidene-fluoride-ethylene tetrafluoride-perfluorovinyl methylether copolymers can be used at temperatures down to −30° C. in staticsealing applications, and down to −25° C. in dynamic sealingapplications, but even this falls short of cold resistance requirementstoday. Apart from their cold resistance, these copolymers have the samedrawbacks as vinylidene fluoride-propylene hexafluoride copolymers.

[0009] Fluorosilicones have an excellent cold resistance, but aninadequate resistance to amines. In addition, they have a poorresistance to gas permeability and a poor water resistance.

[0010] A need has thus been felt for rubber parts endowed with each ofthe above properties to the desired degree.

SUMMARY OF THE INVENTION

[0011] It is therefore an object of the invention to provide rubberaircraft parts which are endowed with good resistance to jet fuels, jetengine oils, amines and oils, good resistance to gas permeability, goodresistance to heat and water, and also outstanding cold resistance.

[0012] We have found that rubber aircraft parts endowed with goodresistance to jet fuels, jet engine oils, amines and oils, goodresistance to gas permeability, good heat and water resistance, andexcellent cold resistance, can be obtained by using the cured form of acurable composition which includes a perfluoropolyether polymer ofperfluoropolyether backbone having at least one reactive group, acrosslinking agent for crosslinking the polymer, and a silica fillerhaving an average particle size of 0.001 to 10 μm. In addition, we havediscovered that such parts can be imparted with a dramatically improvedlow-temperature sealability at temperatures below the minimum servicetemperatures normally achievable in prior-art low-temperaturefluororubbers, i.e., at −25 to −55° C., particularly in a dynamic state,and can also be imparted with a markedly improved resistance to aminesand other chemicals, thus making it possible to reliably ensure thesealability of fluid line junctions in jet engines.

[0013] Accordingly, the invention provides rubber aircraft parts whichare made of the cured form of a curable composition that includes aperfluoropolyether polymer having a perfluoropolyether backbone and atleast one reactive group, a crosslinking agent for crosslinking thepolymer, and a silica filler having an average particle size of 0.001 to10 μm. The invention also provides a method of using the above curedproduct as a fluid sealing component around a jet engine.

DETAILED DESCRIPTION OF THE INVENTION

[0014] As mentioned above, the rubber aircraft parts of the inventionare made of the cured form of a curable composition which includes aperfluoropolyether polymer, a crosslinking agent and a silica filler.

[0015] Any curable composition of the above type may be used, although acurable fluoropolyether rubber composition containing:

[0016] (A) a linear fluoropolyether compound having at least two alkenylgroups per molecule and a backbone with a perfluoropolyether structure;

[0017] (B) an organosilicon compound having at least two silicon-bondedhydrogen atoms (SiH groups) per molecule;

[0018] (C) a hydrosilylation catalyst; and

[0019] (D) a silica filler

[0020] is especially preferred.

[0021] Component A is a linear fluoropolyether compound having at leasttwo alkenyl groups per molecule and a backbone with a divalentperfluoroalkyl ether structure.

[0022] The perfluoroalkyl ether structure contains a plurality of−C_(d)F_(2d)O— repeating units, the letter d in each unit beingindependently an integer from 1 to 6. Exemplary perfluoroalkyl etherstructures include those of general formula (1) below

(C_(d)F_(2d)O)_(q)  (1)

[0023] wherein q is an integer from 1 to 500, preferably from 2 to 400,and most preferably from 10 to 200.

[0024] Examples of the repeating unit —C_(d)F_(2d)O— represented byabove formula (1) include —CF₂O—, —CF₂CF₂O—, —CF₂CF₂CF₂O—,—CF(CF₃)CF₂O—, —CF₂CF₂CF₂CF₂O—, —CF₂CF₂CF₂CF₂CF₂CF₂O— and —C(CF₃)₂O—. Ofthese, —CF₂O—, —CF₂CF₂O—, —CF₂CF₂CF₂O— and —CF(CF₃)CF₂O— are preferred.More preferably, the perfluoropolyether polymer has a perfluoropolyetherbackbone with a structure of the following general formula:

[0025] wherein n is an integer which is at least 10, and especially 30to 200.

[0026] The perfluoroalkyl ether structure may be composed of only one ofthese types of repeating unit, or may be a combination of two or moresuch types.

[0027] It is advantageous for the alkenyl groups on the linearfluoropolyether compound serving as component A to have 2 to 8 carbons,and preferably 2 to 6 carbons, and to have a CH₂═CH— structure at theend. Illustrative examples include vinyl, allyl, propenyl, isopropenyl,butenyl and hexenyl. Of these, vinyl and allyl are preferred. Thealkenyl groups may be present at intermediate positions on the moleculechain, although it is preferable for them to be bonded to both ends ofthe molecular chain. In the latter case, they may be bonded directly toboth ends of the linear fluoropolyether compound backbone or bonded tothe backbone through divalent linkages such as the following:

[0028] —CH₂—, —CH₂O—, —Y—NR′—CO—.

[0029] Here, Y is —CH₂— or a group of the structural formula (2)

[0030] (wherein the free valence bond may be at the o-, m- orp-position); and R′ is a hydrogen atom or a methyl, phenyl or allylgroup.

[0031] The linear fluoropolyether compound of component A is preferablya linear compound of general formula (3) or (4) below:

CH₂═CH—(X)_(p)-Rf-(X)_(p)—CH═CH₂  (3)

CH₂═CH—(X)_(p)-Q-Rf-Q-(X)_(p)—CH═CH₂  (4).

[0032] In formulas (3) and (4), X is independently —CH₂—, —CH₂O— or—Y—NR′—CO— wherein Y and R′ are as defined above. Rf is a divalentperfluoropolyether structure, and preferably one of above formula (1);that is, of the formula (C_(d)F_(2d)O)_(q). The letter p isindependently 0 or 1. Q is a divalent hydrocarbon group of 1 to 15carbons which may include an ether linkage, such as alkylene groups andether linkage-containing alkylene groups.

[0033] The linear fluoropolyether compound serving as component A of thecurable composition is most preferably a compound of the followinggeneral formula.

[0034] In the formula, X is as defined above; p is independently 0 or 1;r is an integer from 1 to 6; u is an integer from 2 to 6; and m and nare independently integers from 0 to 200.

[0035] The linear fluoropolyether compound has a weight-averagemolecular weight of preferably 4,000 to 100,000, and most preferably1,000 to 50,000.

[0036] Specific examples of the linear fluoropolyether compound includethe following compounds. The letters m and n in these compounds are asdefined above.

[0037] In the practice of the invention, to modify the linearfluoropolyether compound to the desired weight-average molecular weightin accordance with the intended use, the above-described linearfluoropolyether compound may first be subjected to hydrosilylation withan organosilicon compound bearing two SiH groups by means of an ordinarymethod and under ordinary conditions. The resulting chain-extendedproduct can then be used as component A.

[0038] Component B of the curable composition used to make the rubberparts of the invention acts as a crosslinking agent and chain extenderfor component A. Component B is not subject to any particularlimitation, provided it is an organosilicon compound having at least twosilicon-bonded hydrogen atoms on the molecule. However, it is preferably(a) a fluorinated organohydrosiloxane and/or (b) an organosiliconcompound in which every silicon-bonded hydrogen atom belongs to a

[0039] structure.

[0040] The fluorinated organohydrosiloxane (a) has at least onemonovalent perfluorooxyalkyl, monovalent perfluoroalkyl, divalentperfluorooxyalkylene or divalent perfluoroalkylene group per molecule.It has also at least two, and preferably at least three, hydrosilylgroups (SiH), per molecule. Preferred examples of suchperfluorooxyalkyl, perfluoroalkyl, perfluorooxyalkylene andperfluoroalkylene groups include those of the following generalformulas: monovalent perfluoroalkyl groups of the formula

C_(m)F_(2m+1)—

[0041] (wherein the letter m is an integer from 1 to 20, and preferablyfrom 2 to 10),

[0042] divalent perfluoroalkylene groups of the formula

—C_(m)F_(2m)—

[0043] (wherein the letter m is an integer from 1 to 20, and preferablyfrom 2 to 10),

[0044] monovalent perfluorooxyalkyl groups of the formula

[0045] (wherein the letter n is an integer from 1 to 5), and divalentperfluorooxyalkylene groups of the formula

[0046] (wherein {overscore (m+n)} is an integer from 2 to 100).

[0047] The fluorinated organohydrosiloxane may be cyclic or acyclic, andmay also have a three-dimensional network structure. Especiallypreferred fluorinated organohydrosiloxanes are those having on themolecule, as a silicon-bonded monovalent substituent, at least onemonovalent organic group containing a perfluoroalkyl, perfluoroalkylether or perfluoroalkylene group of any of the following generalformulas:

[0048] In the above formulas, R¹ is a preferably C₁₋₁₀, and mostpreferably C₂₆, divalent hydrocarbon group such as an alkylene group(e.g., a methylene, ethylene, propylene, methylethylene, tetramethyleneor hexamethylene group) or an arylene group (e.g., a phenylene group);R² is a hydrogen atom or a preferably C₁₋₈, and most preferably C₁₋₆,monovalent hydrocarbon group having no aliphatic unsaturated bonds; andRf¹ is a monovalent perfluoroalkyl, monovalent perfluorooxyalkyl,divalent perfluorooxyalkylene or divalent perfluoroalkylene group of thegeneral formulas shown above.

[0049] Aside from monovalent organic groups containing a monovalent ordivalent fluorinated substituent (e.g., a perfluoroalkyl,perfluorooxyalkyl, perfluorooxyalkylene or perfluoroalkylene group), thesilicon-bonded monovalent substituent in fluorinatedorganohydrosiloxanes (a) may be a monovalent hydrocarbon group of thesame type as those represented above as R², preferably one free ofaliphatic unsaturated bonds and containing 1 to 8 carbons, andespecially 1 to 6 carbons.

[0050] No particular limitation is imposed on the number of siliconatoms per molecule in the fluorinated organohydrosiloxane, although itis generally about 2 to 60, and preferably about 4 to 30.

[0051] Examples of the fluorinated organohydrogensiloxane (a) includethe following compounds. In the following formulae, Me is methyl and Phis phenyl.

[0052] The organosilicon compound (b) in which every silicon-bondedhydrogen atom belongs to a

[0053] structure preferably has general formula (5) below

[0054] In formula (5), N is a moiety of the following general formula

[0055] wherein the letter c is 1, 2, 3 or 4; each R is independently amonovalent C₁₋₂₀, and preferably C₁₋₆, hydrocarbon; Z is -Q′-M, -Q′-Rf′,-Q′-, -Rf″- or -Q′-Rf″-Q′- (Q′ being a divalent C₁₋₁₅ linkage, Rf′ beinga monovalent perfluoroalkyl or perfluorooxyalkyl group, and Rf″ being adivalent perfluoroalkylene or perfluorooxyalkylene group); the letter sis 1, 2 or 3; the letter t is 1, 2 or 3; and the letters a and b are 0or 1, provided a and b are not both 0.

[0056] R is described later in the specification. Illustrative examplesof Q′ include alkylene groups such as methylene, ethylene, propylene andhexylene groups, as well as these alkylene groups with an ether linkage(—O—) on the chain thereof. The monovalent perfluoroalkyl andperfluorooxyalkyl groups serving as Rf′, and the divalentperfluoroalkylene and perfluorooxyalkylene groups serving as Rf″ aredescribed subsequently.

[0057] Illustrative examples of the above-described organosiliconcompound include compounds of the following formulas, wherein “Me”stands for methyl.

[0058] An organosilicon compound having at least one monovalentperfluoroalkyl or monovalent perfluorooxyalkyl group shown as Rf′, ordivalent perfluoroalkylene or divalent perfluorooxyalkylene group shownas Rf″ per molecule can be used to provide good compatibility withcomponent A, good dispersibility, and good uniformity of the compositionwhen cured.

[0059] Preferred examples of such perfluoroalkyl, perfluorooxyalkyl,perfluoroalkylene and perfluorooxyalkylene groups include those of thefollowing general formulas: monovalent perfluoroalkyl groups of theformula

C_(g)F_(2g+1)—

[0060] (wherein the letter g is an integer from 1 to 20, and preferably2 to 10),

[0061] divalent perfluoroalkylene groups of the formula

—C_(g)F_(2g)—

[0062] (wherein the letter g is an integer from 1 to 20, and preferablyfrom 2 to 10),

[0063] monovalent perfluorooxyalkyl groups of the formula

[0064] (wherein the letter n is an integer from 1 to 5), divalentperfluorooxyalkylene groups of the formula

[0065] (wherein m+n is an integer from 1 to 200), and

—(CF₂O)_(m)—(CF₂CF₂O)_(n)—CF₂—

[0066] (wherein the letters m and n are each integers from 1 to 50).

[0067] These perfluoro(oxy)alkyl and perfluoro(oxy)alkylene groups maybe directly bonded to a silicon atom, or may be bonded to a silicon atomthrough a divalent linkage shown as Q′. Exemplary divalent linkagesinclude alkylene groups, arylene groups, and combinations thereof, aswell as any of these together with an intervening ether-bonding oxygenatom, amide bond, carbonyl bond or the like. The divalent linkage haspreferably 2 to 12 carbons. Illustrative examples include —CH₂CH₂—,—CH₂CH₂CH₂—, —CH₂CH₂CH₂OCH₂—, —CH₂CH₂CH₂—NH—CO—, —CH₂CH₂CH₂—N(Ph)—CO—(Ph being a phenyl group), —CH₂CH₂CH₂—N(CH₃)—CO— and —CH₂CH₂CH₂—O—CO—.

[0068] Illustrative examples of the silicon-bonded monovalenthydrocarbon group R on the organosilicon compound serving as abovecomponent (b) include C₁₋₂₀ hydrocarbon groups such as alkyl groups(e.g., methyl, ethyl, propyl, butyl, hexyl, cyclohexyl, octyl, decyl),aryl groups (e.g., phenyl, tolyl, naphthyl), and aralkyl groups (e.g.,benzyl, phenylethyl).

[0069] The number of silicon atoms per molecule on the organosiliconcompound, although not subject to any particular limitation, isgenerally about 2 to 60, and preferably about 3 to 30.

[0070] Illustrative examples of such organosilicon compounds include thecompounds shown below. The following compounds may be used alone or ascombinations of two or more thereof. In the formulas shown below, “Me”stands for methyl and “Ph” stands for phenyl.

[0071] Component B is generally included in an amount which suppliespreferably 0.5 to 5 moles, and most preferably 1 to 2 moles, ofhydrosilyl groups (SiH) per mole of alkenyl groups (e.g., vinyl, allyl,cycloalkenyl) on component A. Too little component B may make the degreeof crosslinking inadequate, whereas too much may favor chain extensionat the expense of curing, may result in foaming of the composition, ormay be detrimental to the heat resistance, compressive set and otherproperties of the rubber parts ultimately obtained.

[0072] The hydrosilylation catalyst serving as component C is preferablya transition metal, such as a platinum group metal (e.g., platinum,rhodium, palladium), or a transition metal compound. Such compounds aregenerally precious metal compounds, and thus very expensive.Accordingly, the use of platinum compounds which are relatively easy toacquire is advantageous for the purposes of the invention.

[0073] Illustrative, non-limiting, examples of suitable platinumcompounds include hexachloroplatinic acid, complexes ofhexachloroplatinic acid with an olefin such as ethylene, complexes ofhexachloroplatinic acid with an alcohol and vinyl siloxane, and platinumon silica, alumina or carbon.

[0074] Platinum group metal compounds other than platinum compounds thatmay be used include rhodium, ruthenium, iridium and palladium compounds.Specific examples include RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂, RhCl(C₂H₄)₂,Ru₃(CO)₁₂, IrCl(CO)(PPh₃)₂ and Pd(PPh₃)₄, wherein “Ph” stands forphenyl.

[0075] The amount of catalyst used is not subject to any particularlimitation, an ordinary amount of catalyst being sufficient to achievethe desired curing rate. However, use of the catalyst in an amount offrom 0.1 to 1,000 ppm (platinum group metal basis), and especially from0.1 to 500 ppm, relative to the overall curable composition, isadvantageous for economic reasons and for achieving a good curedproduct.

[0076] Component D is a silica filler having an average particle size ofpreferably 0.001 to 10 μm, and most preferably 0.005 to 5 μm. Specificexamples include fumed silica and quartz powder.

[0077] The silica filler is typically used in an amount of 1 to 200parts by weight, and preferably 10 to 100 parts by weight, per 100 partsby weight of the perfluoropolyether polymer serving as component A. Toolittle silica filler results in rubber parts which have a low hardnessand a low strength, whereas too much silica filler gives rubber partswhich have a low strength and a low elongation.

[0078] If necessary, various additives may be added to the curablecomposition of the invention to enhance its usefulness. Examples of suchadditives include CH₂═CH(R)SiO (wherein R is a hydrogen atom or asubstituted or unsubstituted monovalent hydrocarbon group)unit-containing polysiloxanes (see JP-B 48-10947) and acetylenecompounds (see U.S. Pat. No. 3,445,420 and JP-B 4-3774) added to controlthe curing rate of the curable composition, and ionic compounds of heavymetals (see U.S. Pat. No. 3,532,649).

[0079] The curable composition used in the invention may also have addedthereto a filler other than silica to reduce heat shrinkage duringcuring and lower the thermal expansion coefficient of the elastomerobtained by curing the composition, to enhance certain properties of theinventive rubber parts, including their thermal stability,weatherability, chemical resistance, fire retardance and mechanicalstrength, and to decrease the gas permeability of the rubber parts.Examples of such additional fillers include glass fibers, carbon, metaloxides such as iron oxide, titanium oxide and cerium oxide, and metalcarbonates such as calcium carbonate and magnesium carbonate. Ifnecessary, suitable pigments and dyes may also be added.

[0080] The curable composition used in the invention may be a millabletype material, or it may be a liquid injection molding system (LIMS)type material prepared by mixing two liquid components and curing underapplied heat.

[0081] If a millable type material is used, the requisite components areblended on a two-roll mill, then molded by a suitable molding processsuch as compression molding, transfer molding or injection molding. Themolding temperature is preferably 80 to 180° C., and most preferably 100to 160° C. The molding pressure is preferably 10 to 300 kgf/cm², andmost preferably 20 to 150 kgf/cm².

[0082] If a LIMS type material is used, the liquid components are mixedin suitable amounts, following which the mixture is molded by a suitablemolding process such as compression molding, transfer molding orinjection molding. Injection molding while mixing the liquid componentsprimarily with a LIMS machine is preferred. The molding temperature andpressure are preferably within the same ranges as those indicated abovefor millable type materials. When molding is carried out at above theindicated temperature range, the curing reaction proceeds before thecomposition has fully assumed the desired product shape. The resultingproduct may thus have a defective appearance, such as a flow pattern orweld lines. On the other hand, when molding is carried out at atemperature below 80° C., curing takes more than 1 hour, which may beimpractical in terms of production efficiency.

[0083] Prior to using the curable composition of the invention, thecomposition may first be dissolved to the desired concentration in afluorinated solvent suitable for the intended application and purpose,such as 1,3-bistrifluoromethylbenzene or perfluorooctane.

[0084] The rubber aircraft parts of the invention are made of the curedform of the above-described curable composition. They have goodresistance to jet fuels, jet engine oils, and amines and oils, goodresistance to gas permeability, good heat and water resistance, andexcellent cold resistance. These qualities enable them to be used assealing materials, such as O-rings, face seals, packings and gaskets,and also as other types of rubber parts, including diaphragms andvalves.

EXAMPLES

[0085] Examples of the invention and comparative examples are givenbelow to illustrate the invention, and are not intended to limit thescope thereof.

[0086] In each of Examples 1 to 3 and Comparative Examples 1 to 3 below,test specimens were fabricated and their properties shown in Table 1were measured. The results are shown in Table 1.

[0087] The measurement methods are as follows.

[0088] Original Properties:

[0089] Hardness was measured according to JIS K 6253.

[0090] Tensile strength and elongation was measured according to JIS K6251.

[0091] Heat Resistance:

[0092] The test specimen was kept in a drier at the temperature shown inTable 1 for 70 hours, and then cooled to room temperature. Thereafter,the hardness, tensile strength and elongation were measured in the samemanner as above. The heat resistance is shown as the change from theoriginal property.

[0093] Compression Set:

[0094] Compression set was measured according to JIS K 6262.

[0095] Jet Engine Oil Resistance:

[0096] The test specimen was immersed in Mobil 254 (available from MobilCo., Ltd.) at 200° C. for 70 hours. Then the test specimen was taken outfrom Mobil 254 and fully wiped to remove Mobil 254 from the surface ofthe test specimen. Thereafter, the hardness, tensile strength,elongation and compression set were measured in the same manner as aboveto evaluate the change from the original property.

[0097] Fuel Resistance:

[0098] The test specimen was immersed in Fuel B at 40° C. for 70 hours.Then the test specimen was taken out from Fuel B and fully dried.Thereafter, the hardness, tensile strength, elongation and compressionset were measured in the same manner as above to evaluate the changefrom the original property.

[0099] Solvent Swelling:

[0100] Solvent swelling was measured according to JIS K 6258 by the testspecimen was immersed in the solvent shown in Table 1 at roomtemperature for 168 hours.

[0101] Low-Temperature Torsional Test, TR Test, Low-TemperatureBrittleness by Impact Test:

[0102] They were measured according to JIS K 6261.

[0103] JIS K 6251 Tensile testing methods for vulcanized rubber

[0104] JIS K 6253 Hardness testing methods for rubber, vulcanized orthermoplastic

[0105] JIS K 6258-1993 Testing methods of the effect of liquids forvulcanized rubber

[0106] JIS K 6261 Low temperature testing methods for rubber, vulcanizedor thermoplastic

[0107] JIS K 6262 Permanent set testing methods for rubber, vulcanizedor thermoplastic

Example 1

[0108] Component A (62 g) and Component B (60 g) of the liquidfluororubber SIFEL 3701 (manufactured by Shin-Etsu Chemical Co., Ltd.)having a perfluoropolyether structure were mixed and vacuum degassed.The degassed material was poured into a mold measuring 170×130×2 mm andcompression molded using a molding machine with a 50-ton press at 150°C. and 80 kgf/cm² for 10 minutes to form a 170×130×2 mm sheet-like testpiece. The test piece was post-cured at 200° C. for a period of 4 hours,yielding a finished test specimen.

Example 2

[0109] A test specimen was fabricated in the same way as in Example 1,but using the liquid fluororubber SIFEL 4750 (manufactured by Shin-EtsuChemical Co., Ltd.) having a perfluoropolyether structure.

Example 3

[0110] A test specimen was fabricated in the same way as in Example 1,but using the liquid fluororubber SIFEL 4755 (Shin-Etsu Chemical Co.,Ltd.) having a perfluoropolyether structure.

[0111] The liquid fluororubbers SIFEL 3701, 4750 and 4755 contain theabove-said components A to D.

[0112] Comparative Example 1

[0113] The binary fluororubber Viton E-60C (a vinylidenefluoride-propylene hexafluoride copolymer manufactured by E. I. DuPontde Nemours and Co.) was compression molded using a molding machine witha 50-ton press at 170° C. and 100 kgf/cm² for a period of 15 minutes toform a sheet-like test piece measuring 170×130×2 mm. The test piece wasthen post-cured at 230° C. for 24 hours, yielding a finished testspecimen.

Comparative Example 2

[0114] A test specimen was fabricated in the same way as in ComparativeExample 1, but using the cold-resistant fluororubber Viton GLT (avinylidene fluoride-ethylene tetrafluoride-perfluorovinyl methyl ethercopolymer manufactured by E. I. DuPont de Nemours and Co.).

Comparative Example 3

[0115] The fluorosilicone rubber FE271 (manufactured by Shin-EtsuChemical Co., Ltd) was compression molded using a molding machine with a50-ton press at 170° C. and 100 kgf/cm² for a period of 15 minutes toform a sheet-like test piece measuring 170×130×2 mm. The test piece wasthen post-cured at 200° C. for 24 hours, yielding a finished testspecimen. TABLE 1 Comparative Example Example Tests 1 2 3 1 2 3 Originalproperties Hardness (type A durometer) 70 72 73 71 71 70 Tensilestrength (Mpa) 7.3 6.8 7.8 12.5 15.2 8.9 Elongation (%) 170 130 140 240240 260 Heat 150° C. Change in hardness (%) +1 +1 +1 +2 +1 +2 resistanceChange in tensile strength (%) −5 −4 −3 −1 −2 −10 (70 hours) Change inelongation (%) −7 −6 −7 −5 −3 −4 200° C. Change in hardness (%) +1 +2 +2+1 +2 +2 Change in tensile strength (%) −5 −8 −9 +12 +4 −5 Change inelongation (%) −4 −10 −10 −11 −10 −9 Compression set 150° C. Deformation(%) 9 5 4 9 16 10 (70 hours) 200° C. Deformation (%) 21 14 11 25 36 31Jet engine oil Change in hardness (%) −4 −3 −3 −10 −9 rub- resistanceChange in tensile strength (%) −11 −9 −7 −71 −20 ber (Mobil 254; Changein elongation (%) +12 +5 +7 −63 −32 dis- 200° C. × 70 hrs) Compressionset (%) 31 12 8 58 28 solved Fuel resistance Change in hardness (%) −4−3 −5 −18 −17 −18 (Fuel B;) Change in tensile strength (%) −15 −12 −13−34 −42 −31 40° C. × 70 hrs) Change in elongation (%) −13 −12 −11 −30−20 −29 Compression set (%) 5 3 2 7 8 6 Solvent Toluene Change in volume(%) +5 +4 +6 +20 +19 +32 swelling Ethanol Change in volume (%) +3 +2 +3+70 +85 +8 (room temp. MEK Change in volume (%) +6 +5 +6 +202 +213 +175× 168 hrs) Tributyl Change in volume (%) +7 +6 +6 rubber amine Change involume (%) dissolved Low temperature T2 (° C.) −37 −38 −36 −7 −21 −50torsional test T5 (° C.) −47 −47 −46 −12 −26 −60 T10 (° C.) −50 −51 −51−16 −28 −63 T100 (° C.) −55 −56 −56 −23 −34 <−70 TR test TR10 (° C.) −50−48 −49 −17 −31 −66 TR40 (° C.) −39 −38 −39 −11 −23 −41 Low temperaturebrittleness Brittleness temperature (° C.) −55 −54 −54 −20 −35 <−70 byimpact test

[0116] As is apparent from the results in Table 1, the rubber aircraftparts according to the invention exhibited good resistance to jet fuels,jet engine oils and amines, good cold resistance, good compression setproperties, and good heat resistance.

[0117] The rubber aircraft parts of the invention provide dramaticallyimproved sealability at temperatures below the minimum servicetemperatures normally achievable in prior-art low-temperaturefluororubbers, i.e., at −25 to −55° C., particularly during use in adynamic state. The inventive rubber parts also provide markedly improvedresistance to amines and other chemicals. These qualities enable therubber parts of the invention to ensure the reliable sealability offluid line junctions in jet engines.

[0118] Japanese Patent Application No. 2001-259925 is incorporatedherein by reference.

[0119] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A rubber part for use in an aircraft, which part is made of the curedform of a curable composition comprising: a perfluoropolyether polymerhaving a perfluoropolyether backbone and at least one reactive group, acrosslinking agent for crosslinking the polymer, and a silica fillerhaving an average particle size of 0.001 to 10 μm.
 2. The rubber part ofclaim 1, wherein the curable composition comprising (A) a linearfluoropolyether compound having at least two alkenyl groups per moleculeand a backbone with a perfluoropolyether structure; (B) an organosiliconcompound having at least two silicon-bonded hydrogen atoms (SiH groups)per molecule; (C) a hydrosilylation catalyst; and (D) a silica filler.3. The rubber part of claim 1, wherein the perfluoropolyether backbonehas a structure of —C_(d)F_(2d)O— repeating units, the letter d in eachunit being independently an integer from 1 to
 6. 4. The rubber part ofclaim 1, wherein the linear fluoropolyether compound of component (A) isone represented by the general formula (3) or (4):CH₂═CH—(X)_(p)-Rf-(X)_(p)—CH═CH₂  (3)CH₂═CH—(X)_(p)-Q-Rf-Q-(X)_(p)—CH═CH₂  (4) in which X is independently—CH₂—, —CH₂O— or —Y—NR′—CO— wherein Y is —CH₂— or a group of thestructural formula (2)

(wherein the free valence bond may be at the o-, m- or p-position); andR′ is a hydrogen atom or a methyl, phenyl or allyl group, Rf is adivalent perfluoropolyether structure of the formula (C_(d)F_(2d)O)_(q),wherein the letter d is independently an integer from 1 to 6 and theletter q is an integer from 1 to 500, the letter p is independently 0 or1, and Q is a divalent hydrocarbon group of 1 to 15 carbons which mayinclude an ether linkage, and component (B) is (a) a fluorinatedorganohydrosiloxane and/or (b) an organosilicon compound in which everysilicon-bonded hydrogen atom belongs to a

structure.
 5. A method of using as a fluid sealing component around ajet engine a cured product of a curable composition comprising: aperfluoropolyether polymer having a perfluoropolyether backbone and atleast one reactive group, a crosslinking agent for crosslinking thepolymer, and a silica filler having an average particle size of 0.001 to10 μm.
 6. The method of claim 5, wherein the curable compositioncomprising (A) a linear fluoropolyether compound having at least twoalkenyl groups per molecule and a backbone with a perfluoropolyetherstructure; (B) an organosilicon compound having at least twosilicon-bonded hydrogen atoms (SiH groups) per molecule; (C) ahydrosilylation catalyst; and (D) a silica filler.
 7. The method ofclaim 5, wherein the perfluoropolyether backbone has a structure of—C_(d)F_(2d)O— repeating units, the letter d in each unit beingindependently an integer from 1 to
 6. 8. The method of claim 5, whereinthe linear fluoropolyether compound of component (A) is one representedby the general formula (3) or (4): CH₂═CH—(X)_(p)-Rf-(X)_(p)—CH═CH₂  (3)CH₂═CH—(X)_(p)-Q-Rf-Q-(X)_(p)—CH═CH₂  (4) in which X is independently—CH₂—, —CH₂O— or —Y—NR′—CO— wherein Y is —CH₂— or a group of thestructural formula (2)

(wherein the free valence bond may be at the o-, m- or p-position); andR′ is a hydrogen atom or a methyl, phenyl or allyl group, Rf is adivalent perfluoropolyether structure of the formula (C_(d)F_(2d)O)_(q),wherein the letter d is independently an integer from 1 to 6 and theletter q is an integer from 1 to 500, the letter p is independently 0 or1, and Q is a divalent hydrocarbon group of 1 to 15 carbons which mayinclude an ether linkage, and component (B) is (a) a fluorinatedorganohydrosiloxane and/or (b) an organosilicon compound in which everysilicon-bonded hydrogen atom belongs to a

structure.